In another aspect the invention relates to an improved thermo-acoustic refrigerator, which lends itself readily to use in methods and apparatus of the type referred to in the preceding paragraph, as well as in a variety of other contexts.
In this day and age, with the ever-increasing publicity being given to the concept of “global warming” and means for reducing the effect thereof, much research has been and is being devoted to, and concentrated on, methods and apparatus for improving energy efficiency and the capture of pollutant emissions from, for example, combustion processes, as for example the burning of fossil fuels and the like. With continued exploration activities being directed to locating accessible supplies of gas and oil, much research has also been dedicated to methods and apparatus for the separation and collection of the natural constituents of gases from gas and oil wells. Existing and on-going research has been and is being directed to improving energy efficiency, reduction of what are referred to as sulphur oxide gases (SOx), and especially a reduction in, more preferably the elimination of, unburnt hydro-carbons, carbon monoxide (CO) and oxides of nitrogen (NOx).
With gases which are the product of a combustion process or the natural constituents of gas streams from gas and oil wells, and here reference is made in particular to gases containing CO2 by way of example, in the case of the former such are normally at an elevated temperature, perhaps in the vicinity of 900° Centigrade. One known technique for separating such a mixture of gases into its constituents has been to utilise what is referred to as vapour compression refrigeration. However, a drawback associated with such vapour compression refrigeration is and has been that the compressors which need to be employed in any such process are expensive to both operate and maintain.
As an alternative to vapour compression refrigeration, attempts have been made to substitute vapour compression refrigeration with what is now known as thermo-acoustic refrigeration. In accordance with known techniques, thermo-acoustic refrigerators have been based on the employment of what are referred to as Rijke tubes. However, in practical terms such Rijke tubes have been found to be inefficient in their operation. In an attempt to improve efficiency, methods and apparatus have been adopted using stationary Stirling Hybrid Engines, wherein the moving piston is replaced by a gas piston.